Helical interpolation (G02 Z.. K../G03 Z.. K..)

Helical interpolation is the superposition of a circular interpolation (plane of 1st and 2nd main axes) and a linear motion in the 3rd main axis. The resulting helical motion is executed at constant pitch. The pitch is programmed by the third parameter of the circular interpolation depending on the selected plane.

It is not necessary to define the pitch so that the helix reaches the programmed target point exactly. In this case, the NC kernel calculates a "corrected" pitch taking into consideration the fixed points for start and target points. The corrected pitch approximates to the programmed pitch as closely as possible.

In this case, the helix target point is first calculated based on the programmed pitch. If the calculated target point differs from the programmed target point, correction is required. The criteria for correction is the distance between the programmed target point and the calculated target point viewed in the direction of rotation.

If the distance is less than or equal to π(180°), the target point of the helix is shifted in the opposite direction of rotation towards the programmed target point, i.e. the pitch is increased.

If it is greater than π(180°), the target point of the helix is shifted in the direction of rotation of the programmed target point, i.e. the pitch is reduced.

Example

Principal correction of a helix clockwise (G02) (1st case)

The target point calculated using the programmed pitch P_prog is located within the range of 180° behind the programmed target point (viewed in the direction of rotation).

Correction takes place by increasing the pitch P_corr.

Example

Principal correction of a helix clockwise (G02) (2nd case)

The target point calculated using the programmed pitch P_prog is located within the range of 180° ahead of the programmed target point (viewed in the direction of rotation).

Correction takes place by reducing the pitch P_corr.

Programing Example

Helical interpolation in the XY plane clockwise

The following helix is travelled:

Starting point a:               X-10 Y0 Z0

Target point b:                X0     Y-10  Z-20

Helix centre point I, J:   Zero point

Helix pitch K:         variable

:

N10 G17 G90 X-10 Y0 Z0 F500 G161

N20 G02 X0  Y-10 Z-20  I0   J0   K..

:

Minimum rotation: ¾ → pitch K=26.66

Pitch K greater than or equal to 26.66:

The helix from a to b is generally executed in ¾ rotation because the correction is limited to the maximum possible pitch K = 26.66.

Pitch K < 26.666: